Life Science

What a koala suggests through its stress

A new research method gives insight into the internal world of Australia’s most beloved marsupial

January 25, 2020
a koala stands on a tree and looks left
Threats like habitat loss, chlamydia, dogs, and road accidents contribute to koala stress. [Credit: Pixabay, Pexel | Creative Commons]

For her graduate degree in conservation physiology, Renae Charalambous started what might be the world’s only koala hair salon. 

Koalas get their hair shaved by veterinarians and researchers for a variety of reasons, including easy insertion of catheters to drain urine from their kidneys or fluid from a surgery. In this particular lab-salon hybrid in Australia, the veterinarians saved the hair samples for Charalambous to wrap in aluminum foil and stick in a freezer at Western Sydney University. 

Charalambous saved the frozen hair until she was ready to begin her new take, published in August in The Journal of Visualized Experiments, on an old research method to answer her question: is there a better way to measure stress in koalas?

She thawed each hair sample and washed it to remove impurities. She then pulverized the hair into powder, added various chemicals like methanol and ethanol, then used this hair soup to measure the past three months of the koala’s cortisol — the key hormone that signals stress levels in koalas and many other animals including humans.  

“It’s an awesome, awesome method,” Charalambous said. Testing koala fur can fix a major problem in koala stress research: Conventional methods for measuring the animal’s stress — drawing blood and other fluids from animals held captive in cages — inflict further stress on the animals. 

The fur method not only helped Charalambous understand the internal world of koalas but reveals how these animals interact with their changing environment. Their environment has changed dramatically in the past few decades in Australia and its coastal islands, the only places in the world where koalas live in the wild.

Growing threats

Charalambous says people in the Sydney suburbs don’t typically see koalas, and are therefore out of touch with the growing number of factors that threaten these animals. The city has expanded into wilderness areas to the extent that many backyards now impinge on koala habitats. Koalas will wander into yards, where pet dogs may attack them. Dogs larger than 22 lbs (10kg) are responsible for 96% of koala attacks, according to the Australian Department of Environment and Heritage Protection. These attacks spike in September at the height of the koala breeding season, when they are most mobile. 

Deforestation is another issue. Australia has lost 40% of its original forest within the last 200 years, and the remaining forests are fragmented. Around 5,000 square kilometers (1,930.5 square miles) of virgin bushland and advanced regrowth forests are destroyed annually, wiping out native wildlife. 

Not only are dogs and deforestation an issue, but the development of roads in wilderness areas also bring more harm to koalas. Automobile drivers hit roughly 300 koalas in 2012, according to the Australian Department of Environment and Heritage Protection, and that average number likely could be rising annually with increasing land clearing and road development. 

Taken together, these human-caused activities cause koalas to experience acute stress, an immediate physical response to a dangerous situation to help the organism survive, says Michael Romero, a wildlife stress researcher from Tufts University who was not involved with Charalambous’ or Narayan’s research. 

You probably know the immediate stress response as “fight or flight.” When animals have to invoke mechanisms to cope with stress frequently or over long periods of time, their health declines. Acute stress evolving into chronic stress have made koalas more vulnerable to one of their most common diseases: chlamydia. 

Chlamydia is a bacterial disease spread through sexual intercourse or from mother to offspring. The disease causes blindness, urinary tract infections and reproductive tract infections that can lead to infertility. “It’s fatal if it’s left untreated,” Charalambous said. Added stress hinders the koala’s immune system, making them more susceptible to infection. 

The bushfires in Australia this fall also certainly raised stress levels among koalas. Among other impacts, the fires wiped out an estimated two million acres and killed 60% of the koalas in Port Macquarie — a critical koala habitat in Australia and the world. Charalambous and Phalen both note that the bushfires could add to the chronic stress hindering a koala’s ability to fight chlamydia.

For all these reasons, biologists and wildlife managers, including Charalambous, want to keep tabs on the health and stress levels among koala populations. But the usual invasive methods for measuring koala stress was what held accurate research back. 

Solving Stress 

Koalas prefer being high in trees where they sit away from predators. They feel most secure up there, says David Phalen, a veterinarian who works with koalas at The University of Sydney. So, when researchers put the koalas in cages, particularly ones that are low on the ground, the animals fear for their lives. 

“They think that when they’re restrained or when they’re in a situation where they don’t have control that they’re about to be killed and eaten,” Phalen said, “So any animal that comes into care is quite fearful that they’re going to die.”

Even when researchers don’t keep koalas in cages, gathering fluids from the animals stresses them. Researchers might take blood samples using hypodermic needles and swab koalas’ mouths with cotton swabs to collect fluids. They then measure the cortisol in these samples. But Charalambous noticed spikes in koalas’ cortisol levels at the time of collection, suggesting that the findings are skewed, possibly by stress induced by the data collection experience itself. 

Since hair can be collected through non-invasive means, Charalambous and Narayan thought to use the method on koalas. Using hair to assess an animal’s stress levels has previously been used in humans, cats and grizzly bears. But the protocol to measure stress hormones in koala fur had not been developed or implemented until Charalambous completed her master’s degree work at Western Sydney University under the guidance of Edward Narayan, a stress researcher and koala advocate at the same university. 

Narayan works in the field of conservation biology, which looks at how factors such as pollution, habitat loss and overhunting affect species survival. But Narayan noticed a missing crucial element: the organism’s internal state, such as their cortisol levels. And that factor is particularly relevant in koalas.

“We are subjectively already noticing that koalas are very emotional creatures,” Narayan said. Narayan realized that cortisol could provide one of the best peeks into a koala’s emotional state, since those quantitative measurements tend to correlate with the psychological responses that we as humans experience. 

Less invasive collection methods for measuring koala stress also can provide more accurate indications of their base-line cortisol levels, according to Charalambous. Koala fur reflects cortisol records for the animal’s past three months, such that each hair sample provides a somewhat long-term reading. And the cortisol measurements can help an animal tell their story in a way humans relate to. 

“I think that these kinds of [non-invasive] techniques hold great promise for trying to understand how animals are coping with human-induced changes in the environment,” said Michael Romero, a wildlife stress researcher from Tufts University who was  not involved with Charalambous’ or Narayan’s research. 

The fur collection technique still has some limitations. It’s crucial that hair gatherers don’t accidentally nick the koala’s skin, as blood contaminates the cortisol reading, Charalambous says. Stress measures collected  from fur can also be thrown off if the animal is pregnant.

Still, it’s important that scientists understand how stressed koalas are, especially in modern-day Australia. 

Hearing about the bushfires, chlamydia disease, road accidents and dog attacks plaguing koalas pulls on the heartstrings of people all around the world, but it hits Narayan particularly hard. 

“I feel as an Australian, as a human being, I feel very sad that our native animals are undergoing these situations,” Narayan said. 

The fight for koalas continues. Donors both domestic and abroad gave the Port Macquarie Koala Hospital $1.5 million to build water sources for koalas in fire-devastated areas and to help rehabilitate the environment.  

While koala habitats and quality of life continue to attempt to adapt to a new normal, humans can do their part by paying attention to koalas and listening to what their stress levels tell us about the quality of their lives and environment. As Romero notes, if we’re going to target conservation efforts for species that are at the greatest risk of our own human activities, working with stress might be one of the best ways to do it.

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About the Author

MK Manoylov likes covering trees, the environment, microbes, and all things bugs. MK was the former opinion editor for The Red & Black newspaper and moved to Brooklyn to pursue science journalism. When not writing, you can find MK editing videos or drawing comics.

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